Abbreviations: PMS, N-methylphenazonium methosulfate; DCIP, dichlorophenolindophenol; DCMU, dichlorophenyl-1,1-dimethylurea; Tricine, tris(hydroxymethyl)methylglycine 相似文献
1. 1. Small particles prepared from spinach chloroplasts after treatment with digitonin, exhibited Photosystem I reactions, including phosphorylation, at rates as high as those in chloroplasts, whereas electron flow from water to NADP+ or ferricyanide through Photosystem II was completely lost. Mediators of cyclic electron flow, such as pyocyanine, or N-methylphenazonium methosulfate in red light, had to be reduced to support photophosphorylation.Diaminodurene at high concentrations catalyzed cyclic phosphorylation under anaerobic conditions without addition of a reductant. In fact, addition of ascorbate gave rise to a marked inhibition which was released by addition of a suitable electron acceptor such as methylviologen.
2. 2. Under aerobic conditions a low O2 uptake, observed in the presence of diaminodurene, was stimulated several-fold upon addition of methylviologen and was stimulated again several-fold on further addition of ascorbate. The rate of phosphorylation, however, remained the same. The low P/2e ratio obtained under these conditions was not decreased at lower light intensities.
3. 3. These findings suggest a phosphorylation site associated with cyclic electron flow through Photosystem I without participation of the electron carriers of Photosystem II. A non-cyclic electron flow to O2 can be induced in this system by addition of methylviologen which effectively competes with the electron acceptors of cyclic flow. This non-cyclic electron flow still involves the same phosphorylation site. A scheme for electron transport and for the location of phosphorylation sites in chloroplasts is proposed.
1. 1. Greening barley and pea leaves treated with lincomycin have a reduced chlorophyll content. Lincomycin does not alter the proportion of chlorophyll in chlorophyll-protein complex II (CPII) but greatly reduces that in chlorophyll-protein complex I (CPI).
2. 2. Difference spectra show that chloroplasts from lincomycin-treated leaves are deficient in at least two long wavelength forms of chlorophyll a. These have maxima at 77 K of 683 and 690 nm.
3. 3. The chemically determined P-700/chlorophyll ratio of chloroplasts is unaffected by lincomycin but the photochemical P-700/chlorophyll ratio is less than half of that of the control. It is less affected than the chlorophyll-protein complex I content.
4. 4. Photosystem I activity expressed on a chlorophyll basis is unaffected by lincomycin but the light intensity for half saturation is increased 8-fold.
5. 5. Chlorophyll-protein complex I apoprotein content is reduced by lincomycin. No evidence was found for an accumulation of its precursor(s). The relative abundance of major peptides of 18 000, 15 000 and 12 000 daltons in lincomycin-treated chloroplasts is attributed to a general inhibition of greening and associated membrane formation.
Abbreviations: DCIP, 2,6-dichlorophenolindophenol; CPI, chlorophyll-protein complex I; CPII, chlorophyll-protein complex II; SDS, sodium dodecyl sulphate 相似文献
1. 1. Chloroplasts can be suspended in aqueous/organic mixtures which are liquid at sub-zero temperatures with a good retention of the ability to reduce artificial electron acceptors. The reduction of ferricyanide and 2,6-dichlorophenolindophenol at temperatures above 0δC is about 50% inhibited by 50% (v/v) ethylene glycol. Higher concentrations cause more extensive inhibition.
2. 2. Different solvents were compared on the basis of their ability to cause a given depression of the freezing point of an aqueous solution. Ethylene glycol caused less inhibition of electron transport than glycerol, which in its turn was found to be superior to methanol.
3. 3. The reduction of oxidised 2,3,5,6-tetramethyl-p-phenylenediamine could be measured at −25δC in 40% (v/v) ethylene glycol. Using an acceptor with a high extinction coefficient, methyl purple (a derivative of 2,6-dichlorophenolindophenol) it was possible to observe electron flow at temperatures as low as −40δC in 50% (v/v) ethylene glycol.
4. 4. From studies of the effects of the inhibitors 3(3,4-dichlorophenyl)-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone it is suggested that electron flow from the donor side of Photosystem II to the acceptor side of Photosystem I can occur at temperatures at least as low as −25δC. The ultimate electron donor is presumably water but it was not possible to demonstrate this directly.
Abbreviations: DCIP, 2,6-dichlorophenolindophenol; DAD, 2,3,5,6-tetramethyl-p-phenylenediamine; DCMU, 3(3,4-dichlorophenyl)-1,1-dimethylurea; DBMIB, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone; DMSO, dimethylsulphoxide 相似文献
1. 1. The coupling factor for photophosphorylation is highly exposed and is selectively and rapidly inhibited by the iodination reaction.
2. 2. A loss of Photosystem I activity (NADP reduction) resulted from iodination. Partial reactions indicated the effect was on electron-transport components on the reducing side of Photosystem I. There was also a limited inhibition of methyl viologen reduction.
3. 3. Iodination of intact membranes caused a reduction in rates of Photosystem II-dependent Hill reaction activity. This inhibition could not be explained solely on the basis of iodination effects on electron-transport components involved in the oxidation of water. The implications of these data with respect to previous chloroplast-membrane models are discussed.
Abbreviations: DABS, p-(diazonium)-benzene sulfonic acid; DCMU, 3-(3-4-dichlorophenyl)-1, 1-dimethylurea; DCIP, 2,6-dichlorophenolindophenol; DPC, diphenyl carbazide; PMS, phenazine methosulfate; Tricine, N-Tris-(hydroxymethyl)-methylglycine 相似文献
1. (1) MgCl2 (1–10 mM range) decreases the intersystem transfer but does not modify the partition of absorbed photons between the photosystems. MgCl2 addition causes a simultaneous increase of excitation life time (τ) and of fluorescence intensity (F). The same linear relationship is obtained with or without added Mg2+.
2. (2) The deactivation of Photosystem II by the Photosystem II to Photosystem I transfer increases with the level of reduced Photosystem II traps. When all Photosystem II traps are closed, half of Photosystem II excitons are deactivated by transfer to Photosystem I.
3. (3) From the relative values of the 685-nm fluorescence yield and System II electron transport rate in limiting light, measured with and without MgCl2, the values of rate constants of Photosystem II deactivation were calculated.
4. (4) The intersystem transfer determines a 715-nm variable fluorescence, which is lowered by MgCl2 addition. When this transfer is decreased by MgCl2 the efficiency of the transfer between Photosystem II-connected units is enhanced, and a more sigmoidal fluorescence rise is obtained.
A double-layer model of the thylakoid membrane where each photosystem is restricted to one leaflet is proposed to explain the decrease of the intersystem transfer after adding cations. It is suggested that MgCl2 decreases the thickness of the Photosystem I polar region, increasing the distance between the pigments of the two photosystems. 相似文献
1. 1. A comparison of chloroplasts from which plastoquinone had been extracted with ultraviolet irradiation supports the conclusion that plastoquinone destruction is not the major cause of ultraviolet inhibition of photosynthesis. No photodestruction of chloroplast lipids, carotenoids or soluble proteins by ultraviolet irradiation was detected.
2. 2. Phenazine methosulfate-mediated cyclic photophosphorylation and variable yield fluorescence were inhibited at the same rate as the Hill reaction. Examination of fluorescence emission spectra of chloroplasts and whole algal cells revealed decreases in both the 685-nm and long-wavelength emission peaks.
3. 3. Digestion of chloroplasts with lipase decreased fluorescence in a manner similar to ultraviolet irradiation. Hill reaction activity was also inhibited by lipase digestion.
4. 4. It is concluded that the inhibition of photosynthesis by ultraviolet irradiation is most likely due to a disruption of the structural integrity of the lamellar membranes which results in the loss of System II activity and associated reactions.
Abbreviations: DCIP, 2,6-dichlorphenolindophenol; DCMU, 3-(3,4-dichlorophenyl)-1,1-dimethylurea; CCCP, m-chlorocyanocarbonylphenylhydrazone; PMS, phenazine methosulfate 相似文献
1. 1. The relationship between temperature and Hill reaction activity has been investigated in chloroplasts isolated from barley (Hordeum vulgare L. cv. Abyssinian).
2. 2. An Arrhenius plot of the photoreduction of 2,6-dichlorophenolindophenol (DCIP) showed no change in slope over the temperature range 2–38 °C. The apparent Arrhenius activation energy (Ea) for the reaction was 48.1 kJ/mol.
3. 3. In the presence of an uncoupler of photophosphorylation, methylamine, the Ea for DCIP photoreduction went through a series of changes as the temperature was increased. Changes were found at 9, 20, 29 and 36 °C. The Ea was highest below 9 °C at 63.7 kJ/mol. Between 9 and 20 °C the Ea decreased to 40.4 kJ/mol and again to 20.2 kJ/mol between 20 and 29 °C. Between 29 and 36 °C there was no further increase in activity with increasing temperature. The temperature-induced changes at 9, 20 and 29 °C were reversible. At temperatures above 36 °C (2 min) a thermal and largely irreversible inactivation of the Hill reaction occurred.
4. 4. Temperature-induced changes in Ea were also found when ferricyanide was substituted for DCIP or gramicidin D for methylamine. The addition of an uncoupler of photophosphorylation was not required to demonstrate temperature-induced changes in DCIP photoreduction following the exposure of the chloroplasts to a low concentration of cations.
5. 5. The photoreduction of the lipophilic acceptor, oxidized 2, 3, 5, 6-tetramethyl-p-phenylenediamine, also showed changes in Ea in the absence of an uncoupler.
6. 6. The temperature-induced changes in Hill activity at 9 and 29 °C coincided with temperature-induced changes in the fluidity of chloroplast thylakoid membranes as detected by measurements of electron spin resonance spectra. It is suggested that the temperature-induced changes in the properties and activity of chloroplast membranes are part of a control mechanism for regulation of chloroplast development and photosynthesis by temperature.
Abbreviations: DADox, oxidized 2,3,5,6-tetramethyl-p-phenylenediamine; DCIP, 2,6-dichlorophenolindophenol; 16NS, 3-oxazolidenyloxy-2-(14-carbmethoxytetradecyl)-2-ethyl-4,4-dimethyl; Ea, Arrhenius activation energy 相似文献
1. 1. The mechanism of the photooxidation of ascorbate and of Mn2+ by isolated chloroplasts was reinvestigated.
2. 2. Our results suggest that ascorbate or Mn2+ oxidation is the result of the Photosystem I-mediated production of the radical superoxide, and that neither ascorbate nor Mn2+ compete with water as electron donors to Photosystem II nor affect the rate of electron transport through the two photosystems: The radical superoxide is formed as a result of the autooxidation of the reduced forms of low potential electron acceptors, such as methylviologen, diquat, napthaquinone, or ferredoxin.
3. 3. In the absence of ascorbate or Mn2+ the superoxide formed dismutases either spontaneously or enzymatically producing O2 and H2O2. In the presence of ascorbate or Mn2+, however, the superoxide is reduced to H2O2 with no formation of O2. Consequently, in the absence of reducing compounds, in the reaction H2O to low potential acceptor one O2 (net) is taken up per four electrons transported where as in the presence of ascorbate, Mn2+ or other suitable reductants up to three molecules O2 can be taken up per four electrons transported.
4. 4. This interpretation is supported by the following observations: (a) in a chloroplast-free model system containing NADPH and ferredoxin-NADP reductase, methylviologen can be reduced to a free radical which is autooxidizable in the presence of O2; the addition of ascorbate or Mn2+ to this system results in a two fold stimulation of O2 uptake, with no stimulation of NADPH oxidation. The stimulation of O2 uptake is inhibited by the enzyme superoxide dismutase; (b) the stimulation of light-dependent O2 uptake in the system H2O → methylviologen in chloroplasts is likewise inhibited by the enzyme superoxide dismutase.
5. 5. In Class II chloroplasts in the system H2O → NADP upon the addition of ascorbate or Mn2+ an apparent inhibition of O2 evolution is observed. This is explained by the interaction of these reductants with the superoxide formed by the autooxidation of ferredoxin, a reaction which proceeds simultaneously with the photoreduction of NADP. Such an effect usually does not occur in Class I chloroplasts in which the enzyme superoxide dismutase is presumably more active than in Class II chloroplasts.
6. 6. It is proposed that since in the Photosystem I-mediated reaction from reduced 2,4-dichlorophenolindophenol to such low potential electron acceptor as methylviologen, superoxide is formed and results in the oxidation of the ascorbate present in the system, the ratio ATP/2e in this system (when the rate of electron flow is based on the rate of O2 uptake) should be revised in the upward direction.
Abbreviations: DCMU, 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea; HEPES, hydroxyethyl-piperazineethanesulfonic acid; MES, (N-morpholino)ethanesulfonic acid; DCIP, 2,4-dichlorophenol-indophenol 相似文献
1. 1. The kinetics of light-induced absorbance changes due to oxidation and reduction of cytochromes were measured in a suspension of intact cells of the unicellular red alga Porphyridium aerugineum. Absorbance changes in the region 540–570 nm upon alternating far-red light and darkness indicated the oxidation of cytochrome ƒ and reduction of cytochrome b563 upon illumination. The relative efficiencies of far-red and orange light indicated that both reactions were driven by Photosystem I.
2. 2. Experiments with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), with anaerobic cells and in alternating far-red and orange light indicated that cytochrome b563 reacts in a cyclic chain around Photosystem I, and that the reduced cytochrome does not react with oxygen or with another oxidized product of Photosystem II. The quantum requirement for the photoreduction was about 6 quanta/equiv at 700 nm. A low concentration of N-methylphenazonium methosulphate (PMS) enhanced the rate of reoxidation of cytochrome b563 in the dark. In the presence of higher concentrations of PMS a photooxidation, driven by Photosystem I, instead of reduction was observed. These observations suggest that PMS enhances the rate of reactions between reduced cytochrome b563 and oxidized products of Photosystem I.
3. 3. In the presence of carbonylcyanide m-chlorophenylhydrazone (CCCP) a light-induced decrease of absorption at 560 nm occurred. Spectral evidence suggested the photooxidation of cytochrome b559 under these conditions. Inhibition by DCMU and a relatively efficient action of orange light suggested that this photooxidation is driven by Photosystem II.
Abbreviations: DBMIB, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone; DCMU, 3-(3,4-dichlorophenyl)-1,1-dimethylurea; CCCP, carbonylcyanide m-chlorophenylhydrazone; FCCP, carbonylcyanide p-trifluoromethoxyphenylhydrazone; P700, chlorophyllous pigment absorbing at 700 nm, primary electron donor of Photosystem I; PMS, N-methylphenazonium methosulphate 相似文献
1. 1. The steady-state fluorescence yield of Chlorella pyrenoidosa is strongly affected by CO2 concentration: the yield is approximately 2-fold higher in the presence than in the absence of CO2. During induction, in the presence of saturating CO2, accelerating oxygen evolution is paralleled by rising fluorescence (M2-P3 transient); in the absence of CO2, fluorescence yield remains at the low M2 level.
2. 2. Both illumination and CO2 content are important in determining the steady-state fluorescence yield: at lower illuminations, lower concentrations of CO2 are required to obtain a maximum fluorescence yield.
3. 3. The slow fluorescence transients are not affected directly by pH but only indirectly through the CO2 concentration.
4. 4. The CO2-dependent fluorescence rise (M2-P3 transient) is most readily observed in cells harvested early in the light period of a synchronous culture, but it can also be elicited in cells harvested during the dark period.
5. 5. Addition of 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU) to CO2-deprived cells raises the fluorescence yield approximately 4-fold, that is to the same high level as cells supplied with CO2 and DCMU.
6. 6. The effects of CO2 provide a new example of a marked parallelism between photosynthetic electron transport and fluorescence. To explain such parallelism, it seems necessary to postulate large changes in the de-excitation processes within Photosystem II units or in the distribution of excitation between Photosystems I and II.
Abbreviations: DCMU, 3-(3,4-dichlorophenyl)-1, 1-dimethylurea; FCCP, carbonyl cyanide p-trifluoromethoxyphenylhydrazone; PMS, phenazine methosulfate 相似文献
1. 1. A simple kinetic analysis of light-induced proton uptake into chloroplasts is presented. It is derived from a model of the reaction in which the incoming proton is obligatorily bound by an intra-chloroplast component, and allows quantitative analysis of the effect into parameters of light and dark rate constants and the availability of the chloroplast component.
2. 2. The effect of the following agents on the derived parameters has been measured: electron and energy transfer inhibitors, uncouplers, NaCl concentration, light intensity and pH.
3. 3. A maximal ratio of 4 protons taken up per electron transported has been observed, using ferricyanide as an electron acceptor.
4. 4. A stimulation of light-induced proton uptake by phosphate or arsenate, ADP and Mg has been observed. It was not sensitive to concentrations of Dio-9, which eliminated ATP synthesis.
5. 5. The results are seen as inconsistent with the chemiosmotic theory of energy coupling as presently presented. It is suggested that they may be interpreted in terms of a model in which the function of the proton pump is to enable co-transport into the chloroplasts of the negatively charged complex of phosphate, ADP and Mg.
Abbreviations: BDHB, n-butyl-3,5-diiodo-4-hydroxybenzoate; DCMU, (3,4-dichlorophenyl)-1,1-dimethylurea; diquat, 1,1′-ethylene-2,2′-dipyridylium dibromide; FCCP, carbonyl cyanide p-trifluoro-methoxy-phenylhydrazone; HQNO, 2-n-heptyl-4-hydroxyquinoline-N-oxide; PMS, phenazine methosulfate 相似文献
1. 1. In isolated chloroplasts with intact envelopes strong fluorescence quenching upon prolonged illumination with red light is accompanied by an absorbance increase. Both effects are reversed by uncoupling with cyclohexylammonium chloride.
2. 2. The fluorescence quenching is reversed in the dark with kinetics very similar to those of the dark decay of chloroplast shrinkage.
3. 3. In intact leaves under strong illumination with red light in CO2-free air a low level of variable fluorescence and a strong shrinkage response are observed. Carbon dioxide was found to increase fluorescence and to inhibit shrinkage.
4. 4. Under nitrogen, CO2 caused fluorescence quenching and shrinkage increase at low concentrations. At higher CO2 levels fluorescence was increased and shrinkage decreased.
5. 5. In the presence of CO2, the steady-state yield of fluorescence was lower under nitrogen than under air, whereas chloroplast shrinkage was stimulated in nitrogen and suppressed in air.
6. 6. These results demonstrate that the fluorescence yield does not only depend on the redox state of the quencher Q, but to a large degree also on the high-energy state of the thylakoid system associated with photophosphorylation.
Abbreviations: DCMU, 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea 相似文献
1. (1) In dark-adapted chloroplasts (i.e. in States S0+S1 according to Kok, B., Forbush, B. and McGloin, M. (1970) Photochem. Photobiol. 11, 457–475), Q, reduced by a flash at low temperature, is reoxidized by a secondary acceptor and the positive charge is stabilized on the Photosystem II donor Z. Although this reaction is strongly temperature dependent, it still occurs very slowly at −60°C.
2. (2) When chloroplasts are placed in the S2+S3 states by a two-flash preillumination at room temperature, the reoxidation of Q− after a flash at low temperature is mainly due to a temperature-independent back reaction which occurs with non-exponential kinetics.
3. (3) Long continuous illumination of a frozen sample at −30°C causes 6–7 reducing equivalents to be transferred to the pool. Thus, a sufficient number of oxidizing equivalents should have been generated to produce at least one O2 molecule.
4. (4) A study of the back reaction in the presence of 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) shows the superposition of two distinct non-exponential reactions one temperature dependent, the other temperature independent.
Abbreviations: DCMU; 3(3; 4-dichlorophenyl)-1; 1-dimethylurea 相似文献
1. 1. By varying the redox potential of a chloroplast suspension, we obtained new evidence for an equilibrium between states S0 and S1 in the model of Kok, B., Forbush, B. and McGloin, N. (1970, Photochem. Photobiol. 11, 457–475). The mid-point potential of the S0 to S1 couple is close to that for the pool of the electron acceptor of System II, A to A−.
2. 2. The limiting steps between two consecutive photoreactions of System II in Chlorella and spinach chloroplasts, have been studied.
2.1. (a) The limiting step from S1 to S2 (noted γ1 (Δt)) is not exponential. Its temperature coefficient becomes greater as the reaction proceeds. The shape of the kinetics is an intrinsic property of each center. Chloroplasts fixed with 2% glutaraldehyde, show simple first order kinetics.
2.2. (b) The limiting step from S0 to S1 (γ0 (Δt)) exhibits the same characteristics as γ1 (Δt)).
2.3. (c) The limiting step from S2 to S3 (γ2 (Δt)) shows sigmoidal kinetics; two reactions are involved. One of the reactions exhibits the same properties as γ0 (Δt) and γ1 (Δt).
2.4. (d) The limiting step from S3 to S0 (γ3 (Δt)) is a first order reaction, two times slower than the other transitions. This reaction is interpretated in terms of oxygen release.
3. 3. We also studied the limiting steps in the presence of low concentrations (50 μM) of hydroxylamine. The results favor the binding of two molecules of hydroxylamine to every photochemical center.
Abbreviations: DCIP, dichlorophenolindophenol 相似文献
1. (1) A P-700-chlorophyll a-protein complex, with a ratio of 1 P-700: 38 chlorophyll a: 4 ta-carotene molecules, had similar absorption and fluorescence characteristics to the chlorophyll-protein complex 1 isolated with Triton X-100 from higher plants, green algae and Ecklonia radiata.
2. (2) An orange-brown complex had a chlorophyll a : c2 : fucoxanthin molar ratio of 2 : 1 : 2. This complex had no chlorophyll c1 and contained most of the fucoxanthin present in the chloroplasts. This pigment complex is postulated to be the main light-harvesting complex of brown seaweeds.
3. (3) A green complex had a chlorophyll a : c1 : c2 : violaxanthin molar ratio of 8 : 1 : 1 : 1. This also is a light-harvesting complex.
The absorption and fluorescence spectral characteristics and other physical properties were consistent with the pigments of these three major complexes being bound to protein. Differential extraction of brown algal thylakoids with Triton X-100 showed that a chlorophyll c2-fucoxanthin-protein complex was a minor pigment complex of these thylakoids. 相似文献
1. (1) Reduced PMS at the concentration of 1 μM inhibits the back reaction as effectively as hydroxylamine, suggesting an electron donating function of reduced PMS for System II.
2. (2) The inhibition of the back reaction by CCCP is regenerated to a high degree by oxidized PMS which led to assume a cyclic System II electron flow catalysed by PMS.
3. (3) At concentrations of reduced PMS higher than 1 μM it is shown that both the fast initial emission and more significantly the variable emission are quenched.
Abbreviations: PMS, N-methylphenazonium methosulfate; CCCP, carbonylcyanide m-chlorophenylhydrazone; FCCP, carbonylcyanide p-trifluoromethoxyphenylhydrazone; TMPD, N,N,N′,N′-tetramethyl-p-phenylendiamine; DCMU, 3-(3,4-dichlorophenyl)-1,1-dimethylurea 相似文献
1. 1. Under normal conditions the ANT 2s-catalyzed cycle includes both light reactions.
2. 2. By selective kinetical inhibition of the electron flow through P700—either by histone treatment or by 2,5-dibromo-3-methyl-6-isopropyl-1,4-benzoquinone blockage—the ANT 2s-induced deactivation of S2 and S3 is not significantly changed. Hence, System I activity is not a functional prerequisite for the ANT 2s-catalyzed discharge of S2 and S3.
3. 3. The reciprocal half time of the ANT 2s-induced decay of the relative average oxygen yield per flash, as a function of the time td between the flashes representing the degree of the Acceleration of the Deactivation Reactions of the water-splitting enzyme system (ADRY) effect, is nearly linearly related to the ANT 2s concentration within the range of 10−7–10−6 M.
4. 4. In respect to the mode of action of ANT 2s two different types of mechanism have been discussed: fixed-place mechanism and mobile-catalyst mechanism.
5. 5. Based on the experimental data the conclusion has been drawn that the ADRY agent ANT 2s probably acts as a mobile catalyst.
Abbreviations: ADRY, Acceleration of the Deactivation Reactions of the water-splitting enzyme stystem Y; ANT 2s, 2-(3,4,5-trichloro)anilino-3,5-dinitrothiophene; DCMU, 3-(3,4-dichlorophenyl)-1,1-dimethylurea; DBMIB, 2,5-dibromo-3-methyl-6-isopropyl-1,4-benzoquinone 相似文献